1. Field of the Invention
The present invention relates to the class of devices for sheet feeding, and in particular, to an automatic sheet feeder (ASF) for an ink jet printer.
2. Description of the Related Art
Ink jet printers, which are common peripheral devices for computers, are very popular due to the ease of replacing a disposable ink cartridge as well as for the cheapness and compactness of these devices. The disposable ink cartridge which is detachable from a carriage in an ink jet printer is filled with ink and has a print head mounted on a specific portion of the cartridge. For printing, the print head jets the ink to a sheet through nozzle holes by using pressure and heat.
One example of a conventional automatic sheet feeder has a guide which is movably secured to a knock-up plate, that is, a paper feed plate. The guide is movable to adjust to sheets of different widths and to prevent the sheet from being fed tilted with respect to the feeding direction. At the right side of the automatic sheet feeder body is rotatably mounted a setting lever for enabling a user, by rotating the lever, to set the uppermost one of the sheets piled up on the knock-up plate, that is, to bring the sheet into contact with feeding rollers. The knock-up plate is restrictively rotatable and has a compressing coil spring mounted on the lower side. The uppermost one of the sheets piled up on the knock-up plate is pressed into contact with the feeding rollers by the elastic force of the compression coil spring. Furthermore, the automatic sheet feeder has a sub-plate which is movable to assist the knock-up plate in supporting the sheet. For individual sheet feeding, the guide is rotated so that the sheets are individually fed in sequence.
At a lower portion of the knock-up plate, feeding rollers are mounted on a shaft at a specific distance from the knock-up plate, and these feeding rollers have rubber attached on the outer circumference to maximize frictional force with the sheet. Accordingly, when a driving force from a driver is provided, the shaft rotates the feeding rollers, and the sheet may be fed. In addition, friction pads are attached to the knock-up plate, facing the feeding rollers, to prevent feeding of more than one sheet at a time.
However, this conventional automatic sheet feeder has the disadvantages of complex structure and inherently large size, which makes it difficult to provide a compact sheet feeder. The complexity of the product may cause an increase in assembling time and a failure rate.
Other examples of sheet feeding devices of the contemporary art are seen, for example, in the following U.S. Patents: U.S. Pat. No. 2,204,715, to Wimmer, entitled Sheet Feeding Apparatus; U.S. Pat. No. 2,679,801, to Ford et al., entitled Driving Mechanism for Sheet-Feeding Devices in Duplicating and Like Machines; U.S. Pat. No. 3,599,971, to Morioka, entitled Device for Automatically Feeding Photosensitive Paper in a Copying Machine; U.S. Pat. No. 5,377,970, to Kikuchi, entitled Sheet Feeding Apparatus with Reduced Vibration Separator; U.S. Pat. No. 5,485,991, to Hirano et al., entitled Automatic Sheet Feeding Apparatus; and U.S. Pat. No. 5,527,026, entitled Auto Compensating Paper Feeder. The devices described in these patents are for ditto machines or copiers, however, and are generally designed for papers of a single width. None of these patents deals with an adjustable paper width guide of the kind usually found in ink jet printers for the purpose of allowing feeding of papers of different width without misfeeding involving tilting of the paper. Moreover, several of these patents disclose the use of spring-loaded knock-up or paper feed plates; the spring-loading arrangement adds to the size and complexity of the device.
Based on my observation of the art, I have discovered that what is needed is a sheet feeding device for an ink jet printer having a compact and simple design and reliable operation.